_{RETROCOMPUTING} Antique Computers Run the World _{By Tom Owad}

I was standing in the control room of a power station, staring at the frozen screen of the computer that controls the turbine system. Reset it, and I risked corrupting a hard drive containing the only working copy of the long-obsolete turbine control software. We had called the manufacturer for support and received the simple reply, “We no longer support that model.” No software, no parts, not even any advice was available for a 15-year-old computer responsible for keeping a 500- megawatt power station operational. I hit reset and held my breath, as I watched the system reboot. With the system back online, I made an image of the hard drive and tried to work out the system’s idiosyncrasies so we could build a replacement for it.

The situation is not uncommon. I have another customer that’s currently stockpiling old Macs so they can continue to run a sophisticated custom application they began developing in 1984.

Hobbyists and historians face similar difficulties. Whereas the technology in an antique piece of machinery is visibly apparent, a dead computer tells one very little. The contents of the firmware and the logic of the custom ICs slip away, leaving a dead black box.

I had these problems in mind recently, while devising a system to automate some 1960s manufacturing equipment for a customer. We’ve gone to great lengths to use open source hardware and to ensure that we have all the schematics we’ll need to reproduce the circuit boards if they’re discontinued. One board uses a PIC microcontroller, of which we’re about to order a lifetime supply.

Photograph by Dennis van Weeren

Open source hardware designs are becoming common. Open Circuits ( opencircuits.com) provides downloads and links to schematics and printed circuit board layouts, and program files for numerous open source hardware projects. Opencores.org has a large repository of Verilog and VHDL chip logic designs (known as “cores”). These cores can be loaded onto FPGAs ( field-programmable gate arrays) as they stand, or can be integrated into one’s own design.

Some of these projects are a boon to classic computer enthusiasts who dread the day when their machine boots its last. Syntiac’s FPGA 64 is an entire Commodore 64, written in VHDL (a design language for FPGAs), that can be loaded onto an FPGA or the C-One microcomputer. For Apple

Dennis van Weeren’s tiny Minimig emulates the venerable Amiga 500 personal computer.

users, Alex Freed took the 6502 in Syntiac’s design and combined it with work of his own to create the FPGApple, a single-chip clone of the Apple II.

Dennis van Weeren is nearing completion of his Amiga 500 re-implementation, the Minimig. It boasts an exact re-creation of the Amiga’s custom chipset, and it currently runs on the Xilinx Spartan- 3 starter kit, along with two printed circuit boards containing the M68000 processor and an MMC memory card slot that supports the FAT16 file system and can decode ADF disk images on the fly.

Code is also available for the Z80, 8088, and many other processors and components. The FPGA in the C-One can be reprogrammed to change the system from a Commodore 64 to an Amstrad CPC. A similar FPGA-based computer, the 1chipMSX, is also under development, with plans to support the Amiga, Amstrad CPC, Apple II, Atari ST, and Commodore 64 and VIC- 20 computers.

With the logic of these systems being preserved in open-source VHDL and Verilog files, it may be that if you want a program that will still function 50 years from now, your best bet is to write it on a classic 8-bit microcomputer.

Tom Owad is the owner of Schnitz Technology, a Macintosh consultancy in York, Pa. He spends his days tinkering and learning, and is the owner and webmaster of applefritter.com.

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